Microscopy and single molecule detection in photosynthesis

Progress in various fields of microscopy techniques brought up enormous possibilities to study the photosynthesis down to the level of individual pigment-protein complexes. The aim of this review is to present recent developments in the photosynthesis research obtained using such highly advanced techniques. Three areas of microscopy techniques covering optical microscopy, electron microscopy and scanning probe microscopy are reviewed. Whereas the electron microscopy and scanning probe microscopy are used in photosynthesis mainly for structural studies of photosynthetic pigment-protein complexes, the optical microscopy is used also for functional studies.     

Ultrafast excited state dynamics controlling photochemical isomerization of N-methyl-4-[trans-2-(4-pyridyl)ethenyl]pyridinium coordinated to a {Re I(CO)3(2,2'-bipyridine)} chromophore

Two multifunctional photoactive complexes [Re(Cl)(CO)(3)(MeDpe(+))(2)](2+) and [Re(MeDpe(+))(CO)(3)(bpy)](2+) (MeDpe(+)=N-methyl-4-[trans-2-(4-pyridyl)ethenyl]pyridinium, bpy=2,2'-bipyridine) were synthesized, characterized, and their redox and photonic properties were investigated by cyclic voltammetry; ultraviolet-visible-infrared (UV/Vis/IR) spectroelectrochemistry, stationary UV/Vis and resonance Raman spectroscopy; photolysis; picosecond time-resolved absorption spectroscopy in the visible and infrared regions; and time-resolved resonance Raman spectroscopy. The first reduction step of either complex occurs at about -1.1 V versus Fc/Fc(+) and is localized at MeDpe(+). Reduction alone does not induce a trans-->cis isomerization of MeDpe(+). [Re(Cl)(CO)(3)(MeDpe(+))(2)](2+) is photostable, while [Re(MeDpe(+))(CO)(3)(bpy)](2+) and free MeDpe(+) isomerize under near-UV irradiation. The lowest excited state of [Re(Cl)(CO)(3)(MeDpe(+))(2)](2+) has been identified as the Re(Cl)(CO)(3)-->MeDpe(+ 3)MLCT (MLCT=metal-to-ligand charge transfer), decaying directly to the ground state with lifetimes of approximately 42 (73 %) and approximately 430 ps (27 %). Optical excitation of [Re(MeDpe(+))(CO)(3)(bpy)](2+) leads to population of Re(CO)(3)-->MeDpe(+) and Re(CO)(3)-->bpy (3)MLCT states, from which a MeDpe(+) localized intraligand (3)pipi* excited state ((3)IL) is populated with lifetimes of approximately 0.6 and approximately 10 ps, respectively. The (3)IL state undergoes a approximately 21 ps internal rotation, which eventually produces the cis isomer on a much longer timescale. The different excited-state behavior of the two complexes and the absence of thermodynamically favorable interligand electron transfer in excited [Re(MeDpe(+))(CO)(3)(bpy)](2+) reflect the fine energetic balance between excited states of different orbital origin, which can be tuned by subtle structural variations. The complex [Re(MeDpe(+))(CO)(3)(bpy)](2+) emerges as a prototypical, multifunctional species with complementary redox and photonic behavior.     

Microfluidics for multiplexed MS analysis

Recent advances of microfluidics systems suitable for multiplexed MS analysis are reviewed with respect to fabrication technologies and applications.     

Injection molded microfluidic chips featuring integrated interconnects

An injection molding process for the fabrication of disposable plastic microfluidic chips with a cycle time of 2 min has been designed, developed, and implemented. Of the sixteen commercially available grades of cyclo-olefin copolymer (COC) that were screened for autofluorescence and transparency to ultraviolet (UV) light, Topas 8007 x 10 was identified as the most suitable for production. A robust solid metal mold insert defining the microfluidic channels was rapidly microfabricated using a process that significantly reduces the time required for electroplating. No wear of the insert was observed even after over 1000 cycles. The chips were bonded by thermal fusion using different bonding conditions. Each condition was tested and its suitability evaluated by burst pressure measurements. The COC microfluidic chips feature novel, integrated, reversible, standardized, ready-to-use interconnects that enable operation at pressures up to 15.6 MPa, the highest value reported to date. The suitability of these UV transparent, high pressure-resistant, disposable devices was demonstrated by in situ preparation of a high surface area porous polymer monolith within the channels.     

Monolithic columns with a gradient of functionalities prepared via photoinitiated grafting for separations using capillary electrochromatography

Stationary phases for capillary electrochromatography with a longitudinal gradient of functionalities have been prepared via photoinitiated grafting of polymer chains onto the pore surface of a porous polymer monolith. In order to achieve the desired retention and electroosmotic flow, the hydrophobic poly(butyl methacrylate-co-ethylene dimethacrylate) monolith with optimized porous properties was grafted with a layer of ionizable polymer, poly(2-acrylamido-2-methyl-1-propanesulfonic acid). A moving shutter and a neutral density filter were used to control the dose of UV light received at different locations along the monolith in order to create the longitudinal gradient of functionalities. Formation of the desired gradients was confirmed using electron probe microanalysis of different locations along the column. The preparation technique significantly affects performance in the CEC mode as demonstrated on the separations of a model mixture using columns both with homogeneous distribution of grafts and with a gradient of functionality. Columns grafted with the gradient of functionalities were found superior to those functionalized uniformly. A comparison of the performance of the gradient column with another containing evenly distributed functionalities showed the performance benefits of the "gradient" column.     

Chip electrochromatography

Electrochromatography (EC) in microfluidic chips is emerging as an attractive alternative to capillary electrophoresis (CE) for on-chip separations. This review summarizes recent developments in the rapidly growing area of chip electrochromatography with a focus on "column" technologies. Relevant achievements are summarized according to the types of stationary phase used for the separations including open channels, microfabricated structures, and channels packed with beads or containing a porous monolith. The advantages and disadvantages of each, as well as practical aspects of their application, are discussed. The analytical performance of these devices is demonstrated with separations involving various families of compounds mostly in the reversed-phase chromatographic mode.     

Tetrathiomolybdates of nickel

Summary The complexes [Ni(en)₃]MoS₄, [Ni(dien)₂]MoS₄ and [Ni(phen)₂(MoS₄)]·2H₂O (en = ethylenediamine, dien = diethylenetriamine, phen = 1,10-phenanthroline) were prepared. On the basis of their magnetochemical and spectral properties the compounds can be characterized as octahedral nickel(II) complexes. The complexes were also studied by c.v. Chemical oxidation of [Ni(en)₃]MoS₄ affords [Ni(en)MoS₄]₂SO₄; this complex has been characterized by i.r. and e.p.r. spectroscopy and by magnetic measurements.